Radiation astronomy/Submillimeters

Submillimetre astronomy or submillimeter astronomy is conducted at submillimetre wavelengths of the electromagnetic spectrum. Astronomers place the submillimetre waveband between the far-infrared and microwave wavebands, typically taken to be between a few hundred micrometres and a millimetre. Using submillimetre observations, astronomers examine molecular clouds and dark cloud cores with a goal of clarifying the process of star formation from earliest collapse to stellar birth.

This image shows two young brown dwarfs, objects that fall somewhere between planets and stars in terms of their temperature and mass. Credit: NASA/JPL-Caltech/D. Barrado [CAB/INTA-CSIC].

"This image [at right] shows two young brown dwarfs, objects that fall somewhere between planets and stars in terms of their temperature and mass. Brown dwarfs are cooler and less massive than stars, never igniting the nuclear fires that power their larger cousins, yet they are more massive (and normally warmer) than planets. When brown dwarfs are born, they heat the nearby gas and dust, which enables powerful infrared telescopes like NASA's Spitzer Space Telescope to detect their presence."[1]

"Here we see a long sought-after view of these very young objects, labeled as A and B, which appear as closely-spaced purple-blue and orange-white dots at the very center of this image. The surrounding envelope of cool dust surrounding this nursery can be seen in purple."[1]

"These twins, which were found in the region of the Taurus-Auriga star-formation complex, are the youngest of their kind ever detected. They are also helping astronomers solve a long-standing riddle about how brown dwarfs are formed more like stars or more like planets? Based on these findings, the researchers think they have found the answer: Brown dwarfs form like stars."[1]

"This image combined data from three different telescopes on the ground and in space. Near-infrared observations collected at the Calar Alto Observatory in Spain cover wavelengths of 1.3 and 2.2 microns (rendered as blue). Spitzer's infrared array camera contributed the 4.5-micron (green) and 8.0-micron (yellow) observations, and its multiband imaging photometer added the 24-micron (red) component. The Caltech Submillimeter Observatory in Hawaii made the far-infrared observations at 350 microns (purple)."[1]

"Other important applications of gyrotrons are high-power microwave sources include high resolution radar ranging and imaging in atmospheric and planetary science as well as deep-space and specialized satellite communications and RF drivers for next-generation high-gradient linear accelerators".[3]

A region of the sky called the "Lockman Hole", located in the constellation of Ursa Major, is one of the areas surveyed in infrared light by the Herschel Space Observatory. Credit: ESA/Herschel/SPIRE/HerMES.

"By the words "warm cloud," we refer to the extended continuum emission -- characteristically several arcminutes in extent -- which can be detected as entities in the FIR and submillimeter regions of the spectrum."[7]

"The Herschel Space Observatory has revealed [in the image at top right] how much dark matter it takes to form a new galaxy bursting with stars."[8]

"If you start with too little dark matter, then a developing galaxy would peter out."[9]

"If you have too much, then gas doesn't cool efficiently to form one large galaxy, and you end up with lots of smaller galaxies. But if you have the just the right amount of dark matter, then a galaxy bursting with stars will pop out."[9]

"This remarkable discovery shows that early galaxies go through periods of star formation much more vigorous than in our present-day Milky Way."[10]

"It showcases the importance of infrared astronomy, enabling us to peer behind veils of interstellar dust to see stars in their infancy."[10]

"It turns out that it's much more effective to look at these patterns rather than the individual galaxies."[11]

"This is like looking at a picture in a magazine from a reading distance. You don't notice the individual dots, but you see the big picture. Herschel gives us the big picture of these distant galaxies, showing the influence of dark matter."[11]

"A region of the sky [at second right, the same as in the upper image] called the "Lockman Hole", located in the constellation of Ursa Major, is one of the areas surveyed in infrared light by the Herschel Space Observatory. All of the little dots in this picture are distant galaxies. The pattern of their collective light is what's known as the cosmic infrared background. By studying this pattern, astronomers were able to measure how much dark matter it takes to create a galaxy bursting with young stars."[12]

"Although a complete inventory of chemical species is not available for any source, millimeter and submillimeter spectral line surveys toward a few sources (e.g., Orion BN/KL and Sgr B2) have detected thousands of lines from approximately 100 distinct chemical species (see Sutton et al. 1995; Schilke, Phillips, & Mehringer 1999)."[13]

"The spectrum includes dust continuum, molecular rotation line and atomic fine-structure line emissions."[14]

"Stretching across almost 100 light-years of space, the Snake nebula is located about 11,700 light-years from Earth in the direction of the constellation Ophiuchus."[16]

"In images from NASA's Spitzer Space Telescope, which observes infrared light, it appears as a sinuous, dark tendril against the starry background. It was targeted because it shows the potential to form many massive stars (stars with more than 8 times the mass of our Sun). SMA was used to observe sub-millimetre radiation from the nebula, radiation emitted between the infrared and radio parts of the electromagnetic spectrum."[16]

"The two panels [at right] show the Snake nebula as photographed by the Spitzer and Herschel space telescopes. At mid-infrared wavelengths (the upper panel taken by Spitzer), the thick nebular material blocks light from more distant stars. At far-infrared wavelengths, however (the lower panel taken by Herschel), the nebula glows due to emission from cold dust. The two boxed regions, P1 and P6, were examined in more detail by the Submillimeter Array."[16]

"To learn how stars form, we have to catch them in their earliest phases, while they're still deeply embedded in clouds of gas and dust, and the SMA is an excellent telescope to do so."[17]

"The team studied two specific spots within the Snake nebula, designated P1 and P6. Within those two regions they detected a total of 23 cosmic "seeds" -- faintly glowing spots that will eventually give birth to between one and a few stars. The seeds generally weigh between 5 and 25 times the mass of the Sun, and each spans a few hundred billion kilometres (for comparison the average Earth-Sun distance is 150 million km). The sensitive, high-resolution SMA images not only unveil the small seeds, but also differentiate them in age."[16]

"Previous theories proposed that high-mass stars form within very massive, isolated "cores" weighing at least 100 times the mass of the Sun. These new results show that that is not the case. The data also demonstrate that massive stars aren't born alone but in groups."[16]

"O I, H2O and O2, and H2O and O2 ices have spectral signatures that lie at frequencies where the terrestrial atmospheric absorption prevents their study from ground-based telescopes, even at mountaintop sites."[13]

The "Goddard High Resolution Spectrometer on board the Hubble Space Telescope, [... has been used to observe] interstellar O I λ1356 absorption toward 13 stars and infer that the total abundance of oxygen (gas plus grains) is homogeneous in the vicinity of the Sun and about two-thirds that of the solar value."[13]

The "absorption and reradiation of light by dust in the history of galaxy formation and evolution is [...] the submillimeter extragalactic background light [(EBL). It] has approximately the same integrated energy density as the optical EBL."[18]

"This dramatic new image of cosmic clouds in the constellation of Orion reveals what seems to be a fiery ribbon in the sky. The orange glow represents faint light coming from grains of cold interstellar dust, at wavelengths too long for human eyes to see. It was observed by the ESO-operated Atacama Pathfinder Experiment (APEX) in Chile."[19]

"In this image, the submillimetre-wavelength glow of the dust clouds is overlaid on a view of the region in the more familiar visible light, from the Digitized Sky Survey 2. The large bright cloud in the upper right of the image is the well-known Orion Nebula, also called Messier 42."[19]

As a "cosmic-ray particle is absorbed [it causes] a rapid rise in temperature. Because it is not practical to prevent these events from occurring, it is necessary to understand their behavior so that they can be removed from raw data during analysis, in a process known as deglitching. This is particularly important when a bolometer is operated in a relatively high cosmic-ray flux such as is found on the Earth near the poles, or in space."[20]

"Due to nγ collisions of the ultrarelativistic neutrons with the submillimeter-IR photons, the neutrons with Lorentz factors Γ > Γesc [...] should degrade in the region r ≤ rmx responsible for the low-frequency radiation of [active galactic nuclei] AGN."[21]

"Radio observations at 210 GHz taken by the Bernese Multibeam Radiometer for KOSMA (BEMRAK) [...] at submillimeter wavelengths [show an impulsive component that] starts simultaneously with high-energy (>200 MeV nucleon−1) proton acceleration and the production of pions. The derived radio source size is compact (≤10"), and the emission is cospatial with the location of precipitating flare-accelerated >30 MeV protons as seen in γ-ray imaging."[22]

"Radio observations at 210 GHz taken by the Bernese Multibeam Radiometer for KOSMA (BEMRAK) [of] high-energy particle acceleration during the energetic solar flare of 2003 October 28 [...] at submillimeter wavelengths [reveal] a gradual, long-lasting (>30 minutes) component with large apparent source sizes (~60"). Its spectrum below ~200 GHz is consistent with synchrotron emission from flare-accelerated electrons producing hard X-ray and γ-ray bremsstrahlung assuming a magnetic field strength of ≥200 G in the radio source and a confinement time of the radio-emitting electrons in the source of less than 30 s. [... There is a] close correlation in time and space of radio emission with the production of pions".[22]

Observations of gamma-ray bursts have been made using the SCUBA instrument on the James Clerk Maxwell Telescope.[23]

A "fading counterpart to GRB 980329 at 850 μm [has been found]. [...] the sub-millimeter flux was relatively bright. [...] The radio through sub-millimeter spectrum of GRB 980329 is well fit by a power law with index α = +0.9. However, we cannot exclude a ν1/3 power law attenuated by synchrotron self-absorption."[23]

"The sub-millimeter [...] is where the emission peaks in some bursts [occur] in the days to weeks following the burst. The sub-millimeter emission is not affected by extinction local to the source or interstellar scintillation."[23]

Submillimeter observations

determine "the breaks in the radio to sub-millimeter to optical spectrum so that the spectral shape can be compared to the synchrotron models"[23]

"The BeppoSAX GRB Monitor was triggered on 1998 March 29.156 UT (Frontera et al. 1998a) [GRB 980329]. This was the brightest burst that had been seen simultaneously by the BeppoSAX Wide Field Camera, with a peak flux ~ 6 Crab in the 2-26 keV band. A fading X-ray source 1SAX J0702.6+3850 was found using the BeppoSAX Narrow Field Instruments (in't Zand et al. 1998)."[23]

At right is "[c]olour composite image of Centaurus A [NGC 5128], revealing the lobes and jets emanating from the active galaxy’s central black hole. This is a composite of images obtained with three instruments, operating at very different wavelengths. The 870-micron submillimetre data, from LABOCA on APEX, are shown in orange. X-ray data from the Chandra X-ray Observatory are shown in blue. Visible light data from the Wide Field Imager (WFI) on the MPG/ESO 2.2 m telescope located at La Silla, Chile, show the stars and the galaxy’s characteristic dust lane in close to "true colour"."[24]

The optical blue band is centered at 445 nm, the optical green band is centered at 551 nm, and the optical red is centered at 658 nm. The submillimeter band (Atacama Pathfinder Experiment) in yellow is centered at 870 µm.

The "effective opacity decreases as a+ [the maximum grain radius] increases in [the] radius range [1 to 100 mm], apparently because the larger particles become individually optically thick and so contribute to the mass [the total grain mass of the cometary coma] faster than they contribute to the radiating cross section."[6]

This image composite shows a warped and magnified view of a galaxy discovered by the Herschel Space Observatory. Credit: ESA/NASA/JPL-Caltech/Keck/SMA.

"This image composite shows a warped and magnified view of a galaxy discovered by the Herschel Space Observatory, one of five such galaxies uncovered by the infrared telescope. The galaxy -- referred to as "SDP 81" -- is the yellow dot in the left image taken by Herschel. It can also be seen as the pink smudges in the right image, a composite of ground-based observations showing more detail."[25]

"Herschel was able to find the galaxy, which is buried in dust, because it happens to be positioned behind another galaxy (blue blob at right), which is acting like a cosmic lens to make it appear brighter. The gravity of the foreground galaxy is distorting and magnifying the distant galaxy's light, causing it to appear in multiple places, as seen as the pink smudges. The distant galaxy is so far away that its light took about 11 billion years to reach us."[25]

"Herschel couldn't detect the foreground galaxy, but astronomers were able to spot it in visible light using the W.M. Keck Observatory. Several follow-up observations by ground telescopes helped to get a better view of the distant galaxy. For example, the pink smudges at the right show wavelengths that are even longer than what Herschel sees in the submillimeter portion of the electromagnetic spectrum. Those observations were made by the Smithsonian Astrophysical Observatory's Submillimeter Array in Hawaii."[25]

The Boomerang Nebula is a young planetary nebula and the coldest object found in the Universe so far. Credit: ESA/NASA.

This is an image of Boomerang nebula taken by Hubble Space Telescope. Credit: NASA, ESA and The Hubble Heritage Team (STScI/AURA).

This is an Atacama Large Millimeter/submillimeter Array (ALMA) telescope image of the Boomerang Nebula. Credit: NRAO/AUI/NSF/NASA/STScI/JPL-Caltech.

"The Boomerang Nebula is a young planetary nebula and the coldest object found in the Universe so far. The NASA/ESA Hubble Space Telescope image is yet another example of how Hubble's sharp eye reveals surprising details in celestial objects."[26]

"NASA's Hubble Space Telescope caught the Boomerang Nebula [at second right] in images taken with the Advanced Camera for Surveys in early 2005. This reflecting cloud of dust and gas has two nearly symmetric lobes of matter that are being ejected from a central star. Each lobe of the nebula is nearly one light-year in length, making the total length of the nebula half as long as the distance from our Sun to our nearest neighbors- the Alpha Centauri stellar system, located roughly 4 light-years away. The Boomerang Nebula resides 5,000 light-years from Earth. Hubble's sharp view is able to resolve patterns and ripples in the nebula very close to the central star that are not visible from the ground."[27]

"This NASA/ESA Hubble Space Telescope image [at top right] shows a young planetary nebula known (rather curiously) as the Boomerang Nebula. It is in the constellation of Centaurus, 5000 light-years from Earth. Planetary nebulae form around a bright, central star when it expels gas in the last stages of its life."[26]

"The Boomerang Nebula is one of the Universe's peculiar places. In 1995, using the 15-metre Swedish ESO Submillimetre Telescope in Chile, astronomers Sahai and Nyman revealed that it is the coldest place in the Universe found so far. With a temperature of -272C, it is only 1 degree warmer than absolute zero (the lowest limit for all temperatures). Even the -270C background glow from the Big Bang is warmer than this nebula. It is the only object found so far that has a temperature lower than the background radiation."[26]

"The Hubble telescope took this image in 1998. It shows faint arcs and ghostly filaments embedded within the diffuse gas of the nebula's smooth 'bow tie' lobes. The diffuse bow-tie shape of this nebula makes it quite different from other observed planetary nebulae, which normally have lobes that look more like 'bubbles' blown in the gas. However, the Boomerang Nebula is so young that it may not have had time to develop these structures. Why planetary nebulae have so many different shapes is still a mystery."[26]

"The general bow-tie shape of the Boomerang appears to have been created by a very fierce 500 000 kilometre-per-hour wind blowing ultracold gas away from the dying central star. The star has been losing as much as one-thousandth of a solar mass of material per year for 1500 years. This is 10-100 times more than in other similar objects. The rapid expansion of the nebula has enabled it to become the coldest known region in the Universe."[26]

"The image was exposed for 1000 seconds through a green-yellow filter. The light in the image comes from starlight from the central star reflected by dust particles."[26] The image pixels have been coded blue even though the filter is centered at 606 nm.

"The Boomerang nebula, called the "coldest place in the universe," reveals its true shape to the Atacama Large Millimeter/submillimeter Array (ALMA) telescope. The background blue structure, as seen in visible light by NASA's Hubble Space Telescope, shows a classic double-lobe shape with a very narrow central region. ALMA’s resolution and ability to see the cold gas molecules reveals the nebula’s more elongated shape, as seen in red."[28]

"It was not until after the variable radio source was discovered that infrared observations [of GRB 980329] found a fading counterpart (Klose et al. 1998; Palazzi et al. 1998; Metzger 1998): this indicated that the optical extinction was significant for this source (Larkin et al. 1998; Taylor et al. 1998b), and/or the redshift was large (Fruchter 1999)."[23]

"Starting on 1998 April 5, we made a series of photometry observations of VLA J070238.0+385044 using SCUBA. [...] On April 5.2 UT, we detected the source at 850 μm with a flux density of 5 ± 1.5 mJy. This source was confirmed on April 6.2 with a flux density of 4 ± 1.2 mJy, resulting in an average of 4.5 ± 1 mJy over the two days."[23]

"The NASA Spitzer Space Telescope has obtained the first infrared images of the dust disc surrounding Fomalhaut, the 18th brightest star in the sky. Planets are believed to form from such a flattened disc-like cloud of gas and dust orbiting a star very early in its life. The Spitzer telescope was designed in part to study these circumstellar discs, where the dust particles are so cold that they radiate primarily at infrared wavelengths. Located in the constellation Piscis Austrinus, the parent star and its putative planetary system are found at a distance of 25 light-years."[29]

"Twenty years ago, the Infrared Astronomical Satellite, the first orbiting infrared telescope, detected much more infrared radiation coming from Fomalhaut than was expected for a normal star of this type. The dust is presumed to be debris left over from the formation of a planetary system. However, the satellite did not have adequate spatial resolution to image the dust directly. Subsequent measurements with sub-millimeter radio telescopes suggested that Fomalhaut is surrounded by a huge dust ring 370 astronomical units (an astronomical unit is the average distance between the Sun and Earth), or 34 billion miles (56 billion kilometers) in diameter. This corresponds to a size of nearly five times larger than our own solar system. Moreover, the sub-millimeter observations (far right image) revealed that the ring was inclined 20 degrees from an edge-on view."[29]

"The new images obtained with the multiband imaging photometer onboard Spitzer confirm this general picture, while revealing important new details of Fomalhaut's circumstellar dust. The 70-micron data (red) clearly shows an asymmetry in the dust distribution, with the southern lobe one-third brighter than the northern. Such an unbalanced structure could be produced by a collision between moderate-sized asteroids in the recent past (releasing a localized cloud of dust) or by the steering effects of ring particles by the gravitational influence of an unseen planet."[29]

"At 24 microns (green), the Spitzer image shows that the center of the ring is not empty. [Note that an image of a reference star was subtracted from the Fomalhaut image to reveal the faint disc emission.] Instead, the 'doughnut hole' is filled with warmer dust that extends inward to within at least 10 astronomical units of the parent star. This warm inner disc of dust occupies the region that is most likely to be occupied by planets and may be analogous to our solar system's 'zodiacal cloud' -- but with considerably more dust. One possible explanation for this warmer dust is that comets are being nudged out of the circumstellar ring by the gravitational influence of massive planets. These comets then loop in toward the central star, releasing dust particles just as comets do in our own solar system."[29]

This image from the Herschel Observatory reveals some of the coldest and darkest material in our galaxy. Credit: ESA/NASA/JPL-Caltech.

"This image [at right] from the Herschel Observatory reveals some of the coldest and darkest material in our galaxy. The choppy clouds of gas and dust pictured here are just starting to condense into new stars. The yellow filaments show the coldest dust dotted with the youngest embryonic stars."[30]

"Infrared, or submillimeter, light with a wavelength of 250 microns is represented in blue; 350-micron light in green; and 500-micron light in red. Much of this region of our galaxy would be hidden in visible-light views."[30]

"The area pictured is in the plane of our Milky Way galaxy, 60 degrees from the center. It spans a region 2.1 by 2.1 degrees. This image was taken by Herschel's spectral and photometric imaging receiver."[30]

"This is one of the early spectra obtained with the SPIRE fourier transform spectrometer on Herschel. Shown here is a portion of the SPIRE spectrum of VY Canis Majoris (VY CMa), a red supergiant star near the end of its life, which is ejecting huge quantities of gas and dust into interstellar space. The inset is a SPIRE camera map of VY CMa, in which it appears as a bright compact source near the edge of a large extended cloud."[31]

"The VY CMa spectrum is amazingly rich, with prominent features from carbon monoxide (CO) and water (H2O). More than 200 other spectral features have been identified so far in the full spectrum, and several unidentified features are being investigated. Many of the features are due to water, showing that the star is surrounded by large quantities of hot steam. Observations like these will help to establish a detailed picture of the mass loss from stars and the complex chemistry occurring in their extended envelopes. As in all of the SPIRE spectra, the underlying emission increases towards shorter wavelengths, and is due to the emission from dust grains. The shape of the dust spectrum provides information on the properties of the dust."[31]

"VY Canis Majoris (VY CMa) is a red supergiant star located about 4900 light years from Earth in the constellation Canis Major. It is the largest known star, with a size of 2600 solar radii, and also one of the most luminous, with a luminosity in excess of 100 000 times that of the Sun. The mass of VY CMa lies in the range 30-40 solar masses, and it has a mass-loss rate of 2 x 10-4 solar masses per year."[31]

"The shell of gas it has ejected displays a complex structure; the circumstellar envelope is among the most remarkable chemical laboratories known in the Universe, creating a rich set of organic and inorganic molecules and dust species. Through stellar winds, these inorganic and organic compounds are injected into the interstellar medium, from which new stars orbited by new planets may form. Most of the carbon supporting life on Earth was forged by this kind of evolved star. VY CMa truly is a spectacular object, it is close to the end of its life and could explode as a supernova at any time."[31]

This picture shows a SPIRE image of the galaxy M74 at a wavelength of 250 microns. Credit: ESA and the SPIRE Consortium.

"On 24 June 2009, SPIRE recorded its first images during the in-orbit commissioning phase of the Herschel mission. This picture, made before fine-tuning or in-orbit final calibration was performed, shows a SPIRE image of the galaxy M74 at a wavelength of 250 microns. The image traces emission by dust in clouds where star formation are active, and the nucleus and spiral arms show up clearly. Dust is part of the interstellar material fuelling star formation, and this image effectively shows the reservoirs of gas and dust that are available to be turned into stars in the galaxy. Significantly, the image frame is also filled with many other galaxies which are much more distant and only show up as point sources. There are also some extended structures, possibly due to clouds of dust in our own galaxy."[32]

"M74 (also known as NGC 628) is a face-on spiral galaxy located about 24 million light-years from Earth in the constellation Pisces. Visible light, produced mainly by the stars within the galaxy, reveals a bright nucleus and well-defined spiral arms that contain many small, bright regions where young massive stars have formed recently. The submillimetre SPIRE image traces the cold dust between the stars, and the spiral arms appear much more enhanced. This galaxy also contains many faint dots that are actually distant galaxies in the background and dust radiating at submillimetre wavelengths but are too distant for the structure in the galaxies to be resolved."[32]

This is a colour composite image of RCW120. Credit: ESO/APEX/DSS2/ SuperCosmos/ Deharveng(LAM)/ Zavagno(LAM).

The image at right is a colour "composite image of RCW120. It reveals how an expanding bubble of ionised gas about ten light-years across is causing the surrounding material to collapse into dense clumps where new stars are then formed. The 870-micron submillimetre-wavelength data were taken with the LABOCA camera on the 12-m Atacama Pathfinder Experiment (APEX) telescope. Here, the submillimetre emission is shown as the blue clouds surrounding the reddish glow of the ionised gas (shown with data from the SuperCosmos H-alpha survey). The image also contains data from the Second Generation Digitized Sky Survey (I-band shown in blue, R-band shown in red)."[33]

The HIFI spectrum of the Orion Nebula is superimposed on a Spitzer image of Orion. Credit: ESA, HEXOS and the HIFI Consortium.

"The HIFI spectrum of the Orion Nebula, superimposed on a Spitzer image of Orion. A characteristic feature is the spectral richness: among the organic molecules identified in this spectrum are water, carbon monoxide, formaldehyde, methanol, dimethyl ether, hydrogen cyanide, sulfur oxide, sulfur dioxide and their isotope analogues. It is expected that new molecules will also be identified. This spectrum is the first glimpse at the spectral richness of regions of star and planet formation. It harbors the promise of a deep understanding of the chemistry of space once the complete spectral surveys are available."[34]

"This HIFI spectrum was obtained for the Herschel HEXOS Key Program - a scientific investigation using the Herschel HIFI and PACS instruments to perform full line surveys of five sources in the Orion and Sagittarius B2 molecular clouds."[34]

"[T]he detection of absorption by interstellar hydrogen fluoride (HF) [in the submillimeter band occurs] along the sight line to the submillimeter continuum sources W49N and W51."[35]

"[T]he 1232.4762 GHz J = 1-0 HF transition [has been observed] in the upper sideband of the band 5a receiver."[35]

"HF is the dominant reservoir of fluorine wherever the interstellar H2/atomic H ratio exceeds ~ 1; the unusual behavior of fluorine is explained by its unique thermochemistry, F being the only atom in the periodic table that can react exothermically with H2 to form a hydride."[35]

The observations "toward W49N and W51 [occurred] on 2010 March 22 ... The observations were carried out at three different local oscillator (LO) tunings in order to securely identify the HF line toward both sight lines. The dual beam switch mode (DBS) was used with a reference position located 3' on either side of the source position along an East-West axis. We centered the telescope beam at α =19h10m13.2s, δ = 09°06'12.0" for W49N and α = 19h23m43.9s, δ = 14°30'30.5" for W51 (J2000.0). The total on-source integration time amounts to 222s on each source using the Wide Band Spectrometer (WBS) that offers a spectral resolution of 1.1 MHz (~0.3 km s-1 at 1232 GHz)."[35]

"[T]he first detection of chloronium, H2Cl+, in the interstellar medium, [occurred on March 1 and March 23, 2010,] using the HIFI instrument aboard the Herschel Space Observatory. The 212 − 101 lines of ortho-H235Cl+ and ortho-H237Cl+ are detected in absorption towards NGC 6334I, and the 111 − 000 transition of para-H235Cl+ is detected in absorption towards NGC 6334I and Sgr B2(S)."[36]

"The Antennae Galaxies (also known as NGC 4038 and 4039) are a pair of distorted colliding spiral galaxies about 70 million light-years away, in the constellation of Corvus (The Crow). This view combines ALMA observations, made in two different wavelength ranges during the observatory’s early testing phase, with visible-light observations from the NASA/ESA Hubble Space Telescope."[37]

"The Hubble image is the sharpest view of this object ever taken and serves as the ultimate benchmark in terms of resolution. ALMA observes at much longer wavelengths which makes it much harder to obtain comparably sharp images. However, when the full ALMA array is completed its vision will be up to ten times sharper than Hubble."[37]

"Most of the ALMA test observations used to create this image were made using only twelve antennas working together — far fewer than will be used for the first science observations — and much closer together as well. Both of these factors make the new image just a taster of what is to come. As the observatory grows, the sharpness, speed, and quality of its observations will increase dramatically as more antennas become available and the array grows in size. This is nevertheless the best submillimetre-wavelength image ever taken of the Antennae Galaxies and opens a new window on the submillimetre Universe."[37]

"While visible light — shown here mainly in blue — reveals the newborn stars in the galaxies, ALMA’s view shows us something that cannot be seen at those wavelengths: the clouds of dense cold gas from which new stars form. The ALMA observations — shown here in red, pink and yellow — were made at specific wavelengths of millimetre and submillimetre light (ALMA bands 3 and 7), tuned to detect carbon monoxide molecules in the otherwise invisible hydrogen clouds, where new stars are forming."[37]

"Massive concentrations of gas are found not only in the hearts of the two galaxies but also in the chaotic region where they are colliding. Here, the total amount of gas is billions of times the mass of the Sun — a rich reservoir of material for future generations of stars."[37]

This diagram is a plot of the zenith atmospheric transmission on the summit of Mauna Kea. Credit: PNG crusade bot.

At right is a plot of the zenith atmospheric transmission on the summit of Mauna Kea throughout a range of 1 to 3 THz at a precipitable water vapor level of 0.001 mm. The graph was created using the CSO Atmospheric Transmission Interactive Plotter at the submillimeter wave astronomy site.[38]

This slice through the new ALMA data reveals the shell around the star. Credit: ALMA (ESO/NAOJ/NRAO).

"Calculations were made using the wavelength-dependent complex refractive indices of silicate (Draine 1985), glassy carbon (Edoh 1983), and Tholin (Khare et al. 1984). [...] these materials were chosen as broadly representative of the types of matter thought to be present in comet dust."[6]

"Observations using the Atacama Large Millimeter/submillimeter Array (ALMA) have revealed an unexpected spiral structure in the material around the old star R Sculptoris. This feature has never been seen before and is probably caused by a hidden companion star orbiting the star. This slice through the new ALMA data reveals the shell around the star, which shows up as the outer circular ring, as well as a very clear spiral structure in the inner material."[39] The image band is centered at 870 µm.

An "intense solar flare spectral radiation component, peaking somewhere in the shorter submillimeter to far-infrared range, [is] identified during the 2003 November 4 large flare. The new solar submillimeter telescope, designed to extend the frequency range to above 100 GHz, detected this new component with increasing fluxes between 212 and 405 GHz."[40]

The submillimetre emission detected by SCUBA-2 is being radiated from the Moon itself. Credit: University of British Columbia, Mike Kozubal.

"This is the Moon seen with SCUBA-2, at wavelengths of 0.45 mm (top left) and 0.85 mm (top right). The bottom left shows a combination of the SCUBA-2 images which give the temperature of the lunar surface, where red is warmest. At the lower right is a visible light image taken at the same time."[41]

"While the optical image shows sunlight reflected from the surface of the Moon, the submillimetre emission detected by SCUBA-2 is being radiated from the Moon itself. The SCUBA-2 temperature map shows that the unilluminated side of the Moon is colder (green and blue), with the coldest region (blue) being where the Sun last heated the surface. The Moon was in "waxing gibbous" phase, meaning that it is on its way to becoming full."[41]

"[A]bsorption features in the submillimeter spectrum of Mars ... are due to the H2O (110-101) and 13CO (5-4) rotational transitions."[42]

"The distribution of water in the Martian atmosphere matches a profile of constant, 100% saturation from 10 to 45 km altitude."[42]

"The primary pointing and calibration source was Mars [observations on November 18-20 and 22-24, 1989 UTC], for which we adopted the 0.8-mm flux density S0.8 = 222 Jy (brightness temperature TB = 210 K) on each night."[6]

Jupiter and the Galilean moons are seen with SCUBA-2. Credit: University of British Columbia.

This map shows the distribution of water in the stratosphere of Jupiter as measured with the Herschel space observatory. Credit: Water map: ESA/Herschel/T. Cavali et al.; Jupiter image: NASA/ESA/Reta Beebe (New Mexico State University).

"[F]or wavelengths between 0.35 and 0.45 mm ... the radiances can be matched by models which include NH3 ice particles which are between 30 and 100 µm in size, regardless of the scale height characterizing the cloud."[43]

The map at right "shows the distribution of water in the stratosphere of Jupiter as measured with the Herschel space observatory. White and cyan indicate highest concentration of water, and blue indicates lesser amounts. The map has been superimposed over an image of Jupiter taken at visible wavelengths with the NASA/ESA Hubble Space Telescope."[44]

"The distribution of water clearly shows an asymmetric distribution across the planet: water is more abundant in the southern hemisphere. Based on this and other clues collected with Herschel, astronomers have established that at least 95 percent of the water currently present in Jupiter's stratosphere was supplied by comet Shoemaker-Levy 9, which famously impacted the planet at intermediate southern latitudes in 1994."[44]

"The map is based on spectrometric data collected with the Photodetecting Array Camera and Spectrometer (PACS) instrument on board Herschel around 66.4 microns, a wavelength that corresponds to one of water's many spectral signatures."[44]

"Jupiter and the Galilean moons [are] seen with SCUBA-2 [in the image at the top of this section]. Rather than seeing the sunlight reflected off the surface of these moons, such as Galileo did 400 years ago, this SCUBA-2 image shows the energy being radiated from the moons themselves."[45]

The order of submillimeter intensity appears to be Ganymede, Callisto, Io, and Europa.

"As a demonstration of ALMA's new short wavelength capabilities, the commissioning team released a new image of planet Uranus as it appears in submillimetre wavelength light. The image — obtained with ALMA's shortest wavelength, Band 10 receivers — reveals the icy glow from the planet's atmosphere, which can reach temperatures as low as -224 C (giving Uranus the coldest atmosphere in the Solar System). ALMA's now broader range of capabilities will enable astronomers and planetary scientists to study and monitor temperature changes at different altitudes above the clouds of Uranus and other giant planets in our Solar System."[47]

This submillimeter image is of a ring of dust particles around the star Epsilon Eridani. Credit: Jane Greaves.

The submillimeter "wavelength view [at right] of a ring of dust particles around Epsilon Eridani, taken with the SCUBA camera at the James Clerk Maxwell Telescope. The false-colour scale is brightest where there is more dust. Epsilon Eridani is marked by the star symbol, although the star itself is not seen at submillimetre wavelengths. Pluto's orbit (marking the edge of our Solar System) is shown at the same scale."[48]

"The ring is "strikingly similar" to the outer comet zone in our Solar System, and shows an intriguing bright region that may be particles trapped around a young planet."[48]

"What we see looks just like the comet belt on the outskirts of our Solar System, only younger, [...] It's the first time we've seen anything like this around a star similar to our Sun. In addition, we were amazed to see a bright spot in the ring, which may be dust trapped in orbit around a planet."[48]

"Epsilon Eridani is far more similar to our Sun than either Vega or Fomalhaut."[48]

"This star system is a strong candidate for planets, but if there are planets, it's unlikely there could be life yet. When the Earth was this young, it was still being very heavily bombarded by comets and other debris."[48]

"It is also a star in our local neighbourhood, being only about 10 light years away, which is why we can see so much detail in the new image."[48]

"If an astronomer could have seen what our Solar System looked like four billion years ago, it would have been very much as Epsilon Eridani looks today, [...] This is a star system very like our own, and the first time anyone has found something that truly resembles our Solar System; it's one thing to suspect that it exists, but another to actually see it, and this is the first observational evidence."[49]

"Beyond Pluto in our Solar System is a region containing more than 70,000 large comets, and hundreds of millions of smaller ones, called the "Kuiper belt". The image [...] shows dust particles that the astronomers believe are analogous to our Kuiper belt at the same distance from Epsilon Eridani as the Kuiper belt is from our Sun. Although the image cannot reveal comets directly, the dust that is revealed is believed to be debris from comets."[48]

"Epsilon Eridani's inner region contains about 1,000 times more dust than our Solar System's inner region, which may mean it has about 1,000 times more comets [...]. Epsilon Eridani is believed to be only 500 million years to 1 billion years old; our Sun is estimated to be 4.5 billion years old, and its inner region is believed to have looked very similar at that age."[48]

"The new image -- which is from short-radio wavelengths, and is not an optical picture -- was obtained using the 15-meter James Clerk Maxwell Telescope [JCMT] at the Mauna Kea Observatory in Hilo, Hawaii. The JCMT is the world's largest telescope dedicated to the study of light at "submillimeter" wavelengths. The [...] camera called SCUBA (Submillimeter Common User Bolometer Array), which was built by the Royal Observatory in Edinburgh (which is now the UK Astronomical Technology Centre). SCUBA uses detectors cooled to a tenth of a degree above absolute zero (-273 degrees Celsius) to measure the tiny amounts of heat emission from small dust particles at a wavelength close to one-millimeter."[48]

"The implication is that if there is one system similar to ours at such a close star, presumably there are many others, [...] In the search for life elsewhere in the universe, we have never known where to look before. Now, we are closing in on the right candidates in the search for life."[49]

"A region near the star that is partially evacuated indicates that planets may have formed, [...] the presence of planets is the most likely explanation for the absence of dust in this region because planets absorb the dust when they form."[48]

"There may be a planet stirring up the dust in the ring and causing the bright spot, or it could be the remnants of a massive collision between comets."[50]

This image from the APEX telescope is part of the Taurus Molecular Cloud. Credit: ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey 2. Acknowledgment: Davide De Martin.

"Using the Submillimeter Array, a set of eight radiotelescopes atop Mauna Kea in Hawaii, [it was] found that G0.253+0.016 possesses very few ultra-dense nuggets that could collapse to form stars."[52]

"This image [at right] from the APEX telescope, of part of the Taurus Molecular Cloud, shows a sinuous filament of cosmic dust more than ten light-years long. In it, newborn stars are hidden, and dense clouds of gas are on the verge of collapsing to form yet more stars. The cosmic dust grains are so cold that observations at submillimetre wavelengths, such as these made by the LABOCA camera on APEX, are needed to detect their faint glow. This image shows two regions in the cloud: the upper-right part of the filament shown here is Barnard 211, while the lower-left part is Barnard 213."[53]

"The submillimetre-wavelength observations from the LABOCA camera on APEX, which reveal the heat glow of the cosmic dust grains, are shown here in orange tones. They are superimposed on a visible-light image of the region, which shows the rich background of stars. The bright star above the filament is φ Tauri."[53]

"Observations made with the APEX telescope in submillimetre-wavelength light at a wavelength of 870 µm reveal the cold dusty clouds from which stars form in the Carina Nebula. This site of violent star formation, which plays host to some of the highest-mass stars in our galaxy, is an ideal arena in which to study the interactions between these young stars and their parent molecular clouds."[54]

"The APEX observations, made with its LABOCA camera, are shown here in orange tones, combined with a visible light image from the Curtis Schmidt telescope at the Cerro Tololo Interamerican Observatory. The result is a dramatic, wide-field picture that provides a spectacular view of Carina’s star formation sites. The nebula contains stars equivalent to over 25 000 Suns, and the total mass of gas and dust clouds is that of about 140 000 Suns."[54]

This is a colour composite image of the central region of our Milky Way galaxy. Credit: ESO/APEX/2MASS/A. Eckart et al.

"The centre of our Galaxy, the Milky Way, lies 27,000 light years from Earth. [The Submillimetre Common User Bolometer Array] SCUBA shows us [in the image above] an exotic region of gas clouds, bubbles, and threads, shaped by stars, supernovae, and magnetic fields. The view is blocked at optical wavelengths by the intervening dust. Credit: D. Pierce-Price et al."[55]

"This is a colour composite image [at right] of the central region of our Milky Way galaxy, about 26 000 light years from Earth. Giant clouds of gas and dust are shown in blue, as detected by the LABOCA instrument on the Atacama Pathfinder Experiment (APEX) telescope at submillimetre wavelengths (870 micron). The image also contains near-infrared data from the 2MASS project at K-band (in red), H-band (in green), and J-band (in blue). The image shows a region approximately 100 light-years wide."[56]

This is a composite image of the Whirlpool Galaxy (also known as M51). Credit: Joint Astronomy Centre, University of British Columbia and NASA/HST (STScI).

The image at right is a "composite image of the Whirlpool Galaxy (also known as M51). The green image is from the Hubble Space Telescope and shows the optical wavelength. The submillimetre light detected by SCUBA-2 is shown in red (850 microns) and blue (450 microns). The Whirlpool Galaxy lies at an estimated distance of 31 million light years from Earth in the constellation Canes Venatici."[57]

"This composite image [at right] shows the discovery of the distant galaxy SMM J2135-0102. Left : a view of galaxy cluster MACS J2135-010217 (centre), which is gravitationally lensing SMM J2135-0102. Top right : SMM J2135-0102 was first discovered in submillimetre-wavelength observations (shown in red) with the LABOCA camera on the Atacama Pathfinder Experiment (APEX) telescope. Bottom right : follow-up observations with the Submillimeter Array (in red) revealed the clouds where stars are forming in the galaxy with great precision. Our view of the galaxy is magnified by gravitational lensing, which also produces a doubling of the image ; the apparent eight regions in the Submillimeter Array observations actually represent four distinct regions of star formation in the galaxy."[58]

The "solar submillimeter telescope [(SST) is] at the El Leoncito Observatory located at 2550 m altitude in the Argentina Andes. The SST has a 1.5 m reflector with four 212 GHz and two 405 GHz radiometers operating simultaneously with 5 ms time resolution. The main-beam cluster consists of three 212 GHz beams (about 4 half-power beamwidth) partially overlapping each other and one 405 GHz beam (about 2) in the center of the three".[40]

At left is the Swedish-ESO 15m Submillimeter Telescope (SEST) at ESO's La Silla Observatory, located on the outskirts of the Chilean Atacama Desert, 600 km north of Santiago de Chile and at an altitude of 2400 metres.

The Kölner Observatorium für SubMillimeter Astronomie (KOSMA) is a 3-m radio telescope located at 3,135 m on Gornergrat near Zermatt (Switzerland) in the southern tower (nearest to the camera). Credit: Doc Searls.

This is the KOSMA 3m submillimeter telescope on Gornergrat near Zermatt in Switzerland. Credit: Fachgruppe Physik.

The recent history period dates from around 1,000 b2k to present.

The Kulmhotel Gornergrat, atop Gorgergrat, which is both mountain and ski slope, is also home to two observatories. The Kölner Observatorium für SubMillimeter Astronomie (KOSMA) [at right] is a 3-m radio telescope located at 3,135 m on Gornergrat near Zermatt (Switzerland) in the southern tower (nearest to the camera).

"Because of the good climatic conditions at the altitude of 3135 m (10285 ft), astronomical observatories have been located in both towers of the “Kulmhotel” at Gornergrat since 1967. In 1985, the KOSMA telescope was installed in the southern tower by the Universität zu Köln and, in the course of 1995, replaced by a new dish and mount."[59]

"The KOSMA telescope with its receivers and spectrometers was dedicated to observe interstellar and atmospheric molecular lines in the millimeter and submillimeter wavelength range. After 25 years of a successful era came to an end (June 2nd, 2010). The 3m KOSMA Radio Telescope left the Gornergrat and joined his long journey to Yangbajing / Lhasa / Tibet."[59]

"Chinese and German scientists are establishing an astronomical observatory in a Tibetan county 4,300 meters above sea level."[60]

"Tibet is an ideal location because the water deficit in its air ensures superb atmospheric transparency and creates a comparatively stable environment for research in the areas of astrophysics, high-energy and atmospheric physics."[61]

"The observatory would house a KOSMA 3-meter sub-millimeter-wave telescope, the first of its kind to be used in general astronomical observation in China."[61]

"It will boost China's research capacity in sub-millimeter astronomy and will hopefully provide a platform for astronomical experiments and training on the plateau and in the polar regions."[61]

"Sub-millimeter astronomy refers to astronomical observations carried out in the region of the electromagnetic spectrum with wavelengths from approximately 0.3 to 1 millimeter."[60]

The submillimeter, millimeter, and microwave spectral line catalog is "a computer-accessible catalog of submillimeter, millimeter, and microwave spectral lines in the frequency range between 0 and 10 000GHz (ie wavelengths longer than 30μm)."[62]

"Bolometers are currently the best choice for sensitive direct detection of radiation at wavelengths between 200 μm and 2 mm (e.g., Refs. 1 and 2). [...] a bolometer operates by measuring the heating due to absorbed energy [... It] is sensitive to any type of energy reaching the absorber. [... Filtering does] not prevent cosmic, gamma, and x rays from reaching a bolometer."[20]

At right is the Atacama Submillimeter Telescope Experiment (ASTE). It "is a joint project between Japan and Chile to install and operate a high-precision, 10 m telescope in the Atacama desert for exploration of the southern sky in the sub-millimeter."[4] ASTE has a main reflector surface accuracy of 19 µm (RMS) and a pointing accuracy of 1.2" (RMS) [for both azimuth and elevation]."[4]

ASTE is located at Pampa la Bola (4860 masl) "in the Atacama desert of Northern Chile."[4]

NASA's balloon-carried BLAST sub-millimeter telescope is hoisted into launch position on Dec. 25, 2012, at McMurdo Station in Antarctica. Credit: NASA/Wallops Flight Facility.

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a submillimeter telescope that hangs from a high altitude balloon. It has a 2 meter primary mirror that directs light into bolometer arrays operating at 250, 350, and 500 µm. ... BLAST's primary science goals are:[63]

High-altitude balloons and aircraft can get above much of the atmosphere. The BLAST experiment and SOFIA are two examples, respectively, although SOFIA can also handle near infrared observations.

At left above "NASA's balloon-carried BLAST sub-millimeter telescope is hoisted into launch position on Dec. 25, 2012, at McMurdo Station in Antarctica on a mission to peer into the cosmos."[64] The giant helium-filled balloon is slowly drifting about 36 km above Antarctica. It was "[l]aunched on Tuesday (Dec. 25) from the National Science Foundation's Long Duration Balloon (LDB) facility ... This is the fifth and final mission for BLAST, short for the Balloon-borne Large-Aperture Submillimeter Telescope. ... "BLAST found lots of so-called dark cores in our own Milky Way — dense clouds of cold dust that are supposed to be stars-in-the-making. Based on the number of dark cores, you would expect our galaxy to spawn dozens of new stars each year on average. Yet, the galactic star formation rate is only some four solar masses per year." So why is the stellar birth rate in our Milky Way so low? Astronomers can think of two ways in which a dense cloud of dust is prevented from further contracting into a star: turbulence in the dust, or the collapse-impeding effects of magnetic fields. On its new mission, BLAST should find out which process is to blame. ... [The 1800-kilogram] stratospheric telescope will observe selected star-forming regions in the constellations Vela and Lupus."[65]

This is a panoramic view of the Chajnantor plateau, spanning about 180° from north (on the left) to south (on the right) showing the antennas of the Atacama Large Millimeter Array. Credit:ESO/B. Tafreshi.

This Submillimeter Array (SMA) is located at Mauna Kea Observatory on Mauna Kea, Hawaii. Credit: Skynoir.

The eight radio telescopes of the Smithsonian Submillimeter Array, located at the Mauna Kea Observatory in Hawai'i, are in place. Credit: Afshin Darian.

The most significant limitation to the detection of astronomical emission at submillimetre wavelengths with ground based observatories is atmospheric emission, noise and attenuation. Like the infrared, the submillimetre atmosphere is dominated by numerous water vapour absorption bands and it is only through "windows" between these bands that observations are possible. The ideal submillimetre observing site is dry, cool, has stable weather conditions and is away from urban population centres. There are only a handful of such sites identified, they include Mauna Kea (Hawaii, USA), the Llano de Chajnantor Observatory on the Atacama Plateau (Chile), the South Pole, and Hanla (India). Comparisons show that all four sites are excellent for submillimetre astronomy, and of these sites Mauna Kea is the most established and arguably the most accessible. The Llano de Chajnantor Observatory site hosts the Atacama Pathfinder Experiment (APEX), the largest submillimetre telescope operating in the southern hemisphere, and the world's largest ground based astronomy project, the Atacama Large Millimeter Array (ALMA), an interferometer for submillimetre wavelength observations made of 54 12-metre and 12 7-metre radio telescopes. The Submillimeter Array (SMA) is another interferometer, located at Mauna Kea, consisting of eight 6-metre diameter radio telescopes. The largest existing submillimetre telescope, the James Clerk Maxwell Telescope, is also located on Mauna Kea.

The Caltech Submillimeter Observatory (CSO) is a 10.4-metre (34 ft) diameter submillimeter wavelength telescope situated alongside the 15-metre (49 ft) James Clerk Maxwell Telescope (JCMT) [below] at Mauna Kea Observatory. It is engaged in submillimeter astronomy, of the terahertz radiation band. The CSO and JCMT were combined to form the first submillimeter interferometer.

The Submillimeter Telescope (SMT), formerly known as the Heinrich Hertz Submillimeter Telescope, is a submillimeter wavelength radio telescope located on Mount Graham, Arizona. It is a 10-meter-wide parabolic dish inside a building to protect it from bad weather. The building front doors and roof are opened when the telescope is in use. The dryness of the air around and above Mt. Graham is particulatly vital for [Extremely high frequency] EHF (extremely low wavelength radio) and far-infrared observations - a region of the spectrum where the electromagnetic waves are strongly attenuated by any water vapor or clouds in the air.

The fourth and fifth images at right are the submillimeter array, or the Smithsonian Astrophysical Observatory Submillimeter Array, (SMA) located at Mauna Kea Observatory on Mauna Kea, Hawaii.

The European Space AgencyHerschel Space Observatory deploys the largest mirror ever launched into space and studies radiation in the far infrared and submillimetre wavebands. Rather than an Earth orbit, Herschel entered into a Lissajous orbit around L2, the second Lagrangian point of the Earth-Sun system. L2 is located approximately 1.5 million km from Earth and the placement of Herschel there lessens the interference by infrared and visible radiation from the Earth and Sun. Herschel's mission focuses primarily on the origins of galaxies and galactic formation.

The observatory will sift through star-forming clouds—the "slow cookers" of star ingredients—to trace the path by which potentially life-forming molecules, such as water, form.